AbstractWhat were the geological relations between Calabria and Sardinia before the opening of the Tyrrhenian Sea? It would be premature to reach a definitive conclusion, so we consider (without reaching any conclusions) four major open questions that bear on the original geologic relationships between Sardinia and Calabria, and that are closely interconnected: (1) Was Calabria a single terrane during post-Hercynian time (Mesozoic and Cenozoic), or is it a composite terrane formed by Cenozoic collision of two subterranes, northern and southern? (2) What has the history of subduction under Calabria been? One interpretation envisions an early «Alpine», east-dipping subduction followed by a later «Apennine», west-dipping subduction; an alternative view is that only west-dipping subduction has occurred. (3) Is there a recognizable match between the Hercynian and Mesozoic geology of Sardinia and of Calabria? The Hercynian evolution of Sardinia is now generally understood, although with some open questions. That of Calabria is still poorly known, which makes it hard at this point to use a match of the Hercynian patterns to constrain a pre-Tyrrhenian terrane reconstruction, but the character of Mesozoic carbonate sequences may provide an additional constraint. (4) How was Calabria extended during its rifting away from Sardinia?

AbstractResolving tectono-stratigraphic relationships, critical for using syn-tectonic sedimentation to calibrate time and length scales of processes in the Apennine-Maghrebian orogenic system, is difficult using outcrop data alone. Here two commercially-acquired seismic reflection profiles are used to establish the structure and stratigraphic relationships between the frontal part of the orogenic belt, the foredeep and foreland regions in the offshore continuation of the Apennine system in the northern Ionian sea. Seismic stratigraphic reasoning is used to define an inter-regional intra-Messinian unconformity surface. In the Apulian foreland this is cut by a widespread array of normal faults that are sealed by Plio-Quaternary sediments. The modern foredeep is in part controlled by these faults. On the Apulian shelf the deposystems are broad. However, the modern foredeep and basins developed on the orogenic wedge are only a few km across. Given the proximity of this study area, the tectono-stratigraphic relationships imaged on these seismic lines are likely to provide good analogues for Neogene basins and depositional systems for much of the Apennines onshore. Syntectonic basins are narrow, long-range stratigraphic continuity is likely to be the exception rather than the rule. This challenges some of the assumptions behind existing tectonic models for the Apennines and similar orogens.
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AbstractThis historical perspective provides an overall view of the main steps that led to the acceptance of the concept of mantle exhumation accompanying lithosphere stretching and extreme crustal thinning. We first remember that the presence of exposures of mantle rocks along oceanic spreading ridges was early reported in the 60's due to the results of sediment cores and dredge hauls collected along the Mid-Atlantic Ridge. In the meantime, detailed analysis of the relationships between oceanic sediments of Late Jurassic age and their primary basement in the Apennine ophiolites led many authors to point to the importance of exhumation of mantle rocks on ancient seafloors. By contrast to the thick sections of classical ophiolites (e.g. Oman), the Alpine-Corsican-Appennine ophiolites are characterized by a relatively small amount of mafic rocks (gabbros and basalts), by the absence of any sheeted dyke complex and by the frequent occurrence of oceanic sediments stratigraphically overlying mantle-derived peridotites and associated gabbroic intrusions. They display some of the characteristics of slow-spreading ridge systems, but, due to their highly tectonized character, they have been interpreted successively either as remnants of oceanic fracture zones of «normal» ocean or as remnants of very-poorly organized, «abnormal» oceanic basement. This review shows how the concept of mantle exhumation has been elaborated more or less in the same period both by marine geoscientists and by geologists conducting investigations in ophiolitic units of the Alps-Apennines mountain belt. Dredging and diving results from the Gorringe Bank, the Iberia margin, the Thyrrenian Sea and the Central Atlantic in the 1980's and 1990's provided additional proofs that the mantle is currently exhumed in various oceanic environments, including distal continental margins, back-arc basins and slow-spreading ridges of wide oceans. It is shown finally how renewed cross-information from mountain belts and the oceans, multiplying the examples of sedimentary reworking of mantle material, help better constrain the mechanisms of mantle exhumation. This mechanism progressively appeared as a fundamental step during the processes of extension of both continental and oceanic lithospheres in numerous geological situations worldwide.

AbstractThe Caledonian Moine Thrust belt is a world class example of a foreland propagating fold-and-thrust belt. The late 19th and early 20th century research in this region was seminal in thrust tectonics, alongside contemporaneous studies of the Alps and Apennines. New British Geological Survey syntheses of the Assynt and Ullapool regions of the Moine Thrust Belt recognise previously unappreciated transverse Zone which accommodate sharp lateral changes in the structural architecture of the brittle-ductile thrust belt, and of the ductile thrust nappes to the east of the Moine Thrust. The Traligill Transverse zones transects the classic Assynt Culmination; the Oykel Tranverse Zone constrains the southern boundary of the Cassley Culmination in Moine rocks east of Assynt. Both transverse structures are oriented sub-parallel to the thrust transport direction and are related to pre-existing faults involving basement.

AbstractSouthern England is in the foreland of the Tertiary Alpine deformation, being ∼700 km from the main orogenic zone. The main Alpine deformation in southern England involved maximum compressive stress (σ1) orientated approximately N-S and with the least compressive stress (σ3) being vertical. This generally caused gentle folding, but deformation is relatively intense around reverse-reactivated faults. This stress system changed so the intermediate compressive stress (σ2) became vertical, causing strike-slip faults that are conjugate about N-S. This probably reflects the reduction of the Alpine compression and the reduction of E-W compressive stresses during Atlantic spreading. The maximum horizontal compressive stress (σH) became perturbed to ∼NW-SE across much of north-western Europe, probably during the Neogene, as indicated by the dominant orientation of joints.

AbstractA new proposal attempting to solve the long-debated issue of the polarity of subduction in the Corsica-Northern Apennine system is presented. Models adopting an original W-dipping subduction and models preferring a flip in the polariy of subduction, from E-dipping to W-dipping, encounter major difficulties at a regional scale. It is considered here that the main inconsistencies faced by both models are due to the two-dimensional approach of reconstructions. The Late Cretaceous to Present-Day kinematics of the Central Mediterranean has been reconstructed using the magnetic anomalies in the Atlantic Ocean and assuming a solid connection between Africa and Adria. Oligocene to Present calcalkaline volcanism and backarc extension in the Balearic and Tyrrhenian basins requires the presence of a wide oceanic embayment to the west of the Adriatic Promontory. It follows that the continental collision that gave rise to the Alps s.s. could not continue SW-ward of Adria. The flip of subduction polarity that can be currently observed, going from the Alps, where Africa is overriding Europe, to the Apennines, where the opposite occurs, was likely on original feature since the beginning of convergence. Kinematic reconstructions allow the point along the plate boundary where the flip of polarity occurs to be tracked back in time. Following the N-ward motion of the colliding Adriatic Promontory, the point of polarity flip moved along the plate boundary from Late Cretaceous to Eocene. As a result, areas that previously experienced continental collision were subsequently affected by oceanic subduction. This sequence of events led to the collapse of the Alpine belt of Corsica and to the opening of the Balearic backarc basin above a retreating oceanic subduction. A similar kinematic evolution is currently ongoing in Taiwan. Finally, the Northern Tyrrhenian basin opened when delamination affected the Adriatic continental margin, following the consumption of oceanic lithosphere at the end of Corsica-Sardinia rotation.

Abstracthis paper describes the tectonic evolution of the Col del Lis-Trana Deformation Zone (LTZ), a N-S striking structure located in the internal sector of the northern Cottian Alps, in the hanging-wall of the first-order discontinuity (the Canavese Line) and representing the eastern border of the Alpine wedge. The detailed geological mapping and structural analysis of the two tectonometamorphic Units cropping out in the area has allowed the activity of the LTZ to be defined, related to two late- to post-metamorphic deformation phases (D4 and D5). This activity strongly modified the pre-existing syn-metamorphic structural setting, resulting from three main deformation phases (D1, D2 and D3). The LTZ is defined by i) the clockwise rotation at the macroscale both of syn-metamorphic structural elements and of lithological contacts from E-W to N-S strike directions, and by ii) the structural association of faults, cleavages and folds, mainly related to the reactivation of the pre-existing syn-metamorphic anisotropies. The D4 phase is characterized by the development of N-S major faults and by NNW-SSE and NNE-SSW minor faults, linked in a through-going shear zone with dextral shearing and minor reversal component, whereas the D5 phase is associated with the activity of E-W faults and with the reactivation of the D4-related structures mainly characterized by normal and sinistral-normal movements. The kinematic analysis of the D4-related structures yields a sub-horizontal NE-SW shortening direction, comparable with the regional shortening that affected the Western Alps during the Late Oligocene-Early Miocene and which caused the dextral movements along the Canavese Line. The extensional regime related to the D5 event is interpreted as the effect of the uplift with the subsequent isostatic re-adjustment of the alpine wedge.
Since the LTZ is a very persistent structure (more than 20 km in length) it may be reasonably considered as a deep-rooted shear zone, which could reach 7-10 km of depth. Based on these assumptions the LTZ may be interpreted as a sub-parallel structure of the postulated southern prolongation of the Canavese Line, both representing steep fault strands of a regional dextral transpressive flower structure that bounds the alpine wedge on the internal side.

AbstractIn the Trasimeno Lake area (Umbria Region), several thrust sheets belonging to the Sansepolcro-Monte Filoncio and Rentella Units, are interposed between the Tuscan Nappe (in the hanging-wall) and the Umbria-Romagna Unit (in the footwall). The thrust sheets succession of the Sansepolcro-Monte Filoncio Unit is made up of Rupelian-Chattian Scaglia toscana Fm. and Chattian-Aquitanian foredeep deposits of Macigno Fm.; the base of the siliciclastic succession becomes gradually younger eastward. The compositional mode of the fine-grained rock fragments in the arenaceous turbidites is comparable with that of the upper part of the Macigno Fm. in the Tuscan Nappe.
The succession of the Rentella Unit includes Rupelian-Aquitanian Monte Rentella Fm. and Aquitanian-Burdigalian foredeep siliciclastic turbidites of the Montagnaccia Fm.. In the lower portion of the Montagnaccia Fm. a level of black cherty horizons is present, as detected in all Aquitanian-Burdigalian successions of the Northern Apennines. The compositional mode of the fine-grained rock fragments in the turbidites is comparable with that of Marnoso-Arenacea Fm..
All these data allow an Oligocene-Miocene paleogeographic reconstruction of the Northern Apennines foredeep. Based on the age, the compositional mode and structural position, the Rentella and Sansepolcro-Monte Filoncio Units can be compared to the Carigiola and Acquerino Units cropping out in the Tuscan-Emilian Apennines.

AbstractA new structural setting for the central part of the External Ligurian Briançonnais (CELB) is proposed. CELB is divided into km-scale tectonic units that still preserve pre-Alpine geological features at several stratigraphic levels. Macro-, meso- and microscale primary features, such as paleoescarpments, unconformities and depositional or diagenetic fabrics are thus well preserved and can be still mapped and studied in detail at many stratigraphic levels.
Significant transposition of bedding is recorded only in Upper Cretaceous and Eocene marly limestones and shales and in major km-long shear zones, where intense development of closely spaced tectonic foliations occurred.
Several features indicate that the CELB tectonic evolution took place at shallow crustal levels: 1) strong localization of deformation along the weakest stratigraphic levels; 2) absence of diffuse recrystallization of rocks; 3) minor occurrence or absence of transposition of bedding; 4) kinematic evolution of fold axial plane foliations into frictional slip cleavages.
A gradual decrease in the intensity of deformation from the Internal Ligurian Briançonnais to CELB and Dauphinois Domain is observed, although the boundaries of these three domains correspond, in the study area, to several Km-long, transpressive shear zones whose kinematic role in the evolution of the southern termination of the Western Alps should be carefully considered.

AbstractWe analyse the instrumental seismicity of the Abruzzo region in the period 1981-2003 in order to obtain a catalogue as homogeneous as possible in terms of location procedure and quality of the results. We analyse four temporal datasets: 1981-1991; 1992-1996; 1997-1999 and 2000-2003. The 1981-1991 dataset is taken from the CSTI catalogue, opportunely selected by using quality criteria. The datasets from 1992 to 2003 are relocated by integrating the recordings of the national seismic network with the recordings of the local Abruzzo seismic network (operating from 1992 to 1999). Particular attention is paid to the velocity models, in order to account for the different stratigraphic/tectonic domains which characterize the Abruzzo region. In particular, we used 8 velocity models, applied to stations or groups of stations lying within relatively homogeneous areas. We obtained a database, selected for RMS ≤0.5s and hypocentral errors ≤5 km, of 985 events with 0.5≤M≤4.4 plus two events of moderate magnitude (Mw=5.9, Mw=5.5) corresponding to the largest shocks of the May 1984 Sangro Valley seismic sequence. We also computed 17 new focal mechanisms. The seismotectonic implications mainly concern the thickness of the seismogenic layer. A robust statistical estimate of the base of the seismogenic layer is given by the depth above which the 90% of seismicity occurs (D90). The maximum thickness (15-17 km) is found in the eastern Abruzzo Apennines (surface heat flow ≤40 mW/m2). A thickness of 12-14 km is found in the western Abruzzo Apennines (40< surface heat flow ≤60 mW/m2). The observed depths are consistent with independent rheological data (B-D transition). The connection between the background seismicity and the geometry at depth of the active faults is feasible only rarely (e.g. M. Gorzano normal fault in northern Abruzzo). More often the seismicity is spread within the seismogenic volume. Locally, it concentrates close to structural complexities or defines small seismic sequences activating inherited structures. The active faults south of L'Aquila are almost free from microseismic activity. The new focal mechanisms computed from the 1992-1999 database confirm and reinforce the existence of a dominating extensional regime across the Abruzzo Apennines.

Abstractn the frontal sector of the Central-Southern Apennines, surface geological data integrated with seismic line interpretation provide new constraints into the reconstruction of the structural inheritance of Mesozoic pre-orogenic and Messinian-Pliocene syn-orogenic normal faults on the salient geometry of the Pliocene-Quaternary thrust system.
In the Umbria-Marche-Abruzzi area, pre-orogenic normal faults commonly juxtapose the complete Jurassic succession (about 900 metres in thickness) onto coeval condensed successions (about 50 metres in thickness) deposited over structural highs. In the Sibillini Mts and Gran Sasso area, pre-orogenic normal faults are truncated and rotated into Pliocene thrust-sheets according to simple short-cut trajectories. In particular the foreland-dipping Jurassic normal faults in the Sibillini Mts area have been rotated and reactivated during the thrust propagation forming high-angle blind-thrusts in the east verging overturned folds.
The Maiella anticline, which involves the Mesozoic-Miocene Apulian carbonate succession and the related slope deposits, joins the Central Apennine fold-and-thrust system to the Apulian Chain buried below the allochthonous Units of the Southern Apennines. Seismic line interpretation allowed us to reconstruct the three-dimensional pattern of the Apulian thrusts, oriented N-S, NNW-SSE and E-W, that are parallel to normal faults related to the Pliocene-Quaternary flexural extension in the foreland. Detailed reconstruction of the Setteporte and Monte Taburno structures shows main N-S/NNE-SSW trending thrusts, branching into NW-SE/E-W trending minor thrusts and back-thrusts, characterized by push-up geometry, typically referable to a transpressive deformation and/or to the positive reactivation of normal faults. Moreover, the sharp westward deepening of the base of the Apulian sedimentary succession (from 4.5 to 6.0 sec in TWT), based on the interpretation of the CROP 11 seismic reflection profile, and the concomitant increase in thickness of the Triassic sequence along the Maiella-Casoli transect, suggest the existence of west-dipping (?)Permian-Triassic normal faults that strongly controlled the distribution and thickness variation of syn-rifting sediments. An inversion of the deepest low angle portions of the pre- and syn-orogenic normal faults is in agreement with surface data (i.e., the structural elevation of the carbonate succession in the Casoli-Bomba anticline) and seismic line interpretation (i.e., deep seated location of the base of Apulian sedimentary succession below the same anticline).
In the reconstructed inversion tectonics model, the N-S trending pre-thrusting normal faults are fully inverted as N-S transpressive segments of the salient structures of the chain, whereas, the NW-SE trending thrusts inverted the low angle portion of pre-thrusting normal faults in the middle-lower crust and displaced with a short-cut the normal faults in the upper portion of the crust. As a result, the pattern of the pre-existing normal faults is inherited on the salient structures of the Central and Southern Apennine Chain.

AbstractA multidisciplinary approach on mainly continental carbonate deposits outcropping in the southern part of the Valdelsa Basin has allowed the recognition of two units, the Strove Synthem (STR) and the Campiglia dei Foci Synthem (CDF), both previously attributed altogether to a single indistinct sequence.
The presence of a mammalian fauna suggests that the STR Synthem belongs to the Early-Middle Pleistocene, whereas the CDF Synthem is assigned to Middle Pleistocene because of its stratigraphic position. Lateral correlation with continental deposits cropping out in the adjacent Lower Valdarno Basin suggests an age not younger of the Stage 11 of the isotope scale. A paleopedological study of the soils on the synthems has distinguished two pedogenetic typologies: a Cutanic Alisol (Manganiferric) on Gleyic Vertisol for STR Synthem and a Haplic Cambisol on Rhodic Luvisol on Rhodic Nitisol for CDF Synthem. The different pedogenetic development corroborated the hypothesis of two distinct synthems.
The attitude of the STR Synthem (tilted deposits) in comparison with the CDF Synthem (sub-horizontal bedding) shows that the former was affected by a tectonic phase which ended before the deposition of the latter synthem. The chronostratigraphic attribution of the two synthems allow us to tentatively relate this tectonic phase with the regional Middle Pleistocene tectonic uplift, which caused the present Northern Apennine mountain chain.

AbstractSatellite imageries from Landsat ETM+ and ERS (European Remote Sensing) Radar sensors, together with elevation data collected by the Shuttle Radar Topography Mission (SRTM) in addition to recent and older bibliography, have led to the hypothesis that, before the Late Messinian drawdown of the Mediterranean Sea, the River Nile flowed into the Libyan palaeo-Sirt. The study is still in progress; in this paper data are presented from three areas, showing evidence of palaeo-drainage of Tortonian-Late Messinian age, that could be considered sufficient to delineate the course of the Nile River up to the Gulf of Sirt (fig. 1).

AbstractOne of the most fascinating problems of the Southern Alps is the meaning of the strong structural indentation between the Sothern Alps and the Austroalpine units along N-Giudicarie fault, where the Europe-verging nappe stack of the Alps (Austroalpine and Penninic nappes) and the Africa-verging thrust belt of the Southern Alps face each other and appear sinistrally displaced more than 50 km. Starting from the beginning of ‘900 century, several generations of geologists considered the sinistral slip on the fault responsible of the indentation of the Alps along the Giudicarie lineament, occurred during N-S Neogene compressions. Old and new data, on the contrary, indicate that most of the extensive sinistral displacement affecting the N Giudicarie Lineament originated during late Cretaceous-early Eocene times. The Pre-Adamello structural belt is present only in the internal Lombardy zone, located W of the Adamello massif. This belt is unknown in the Dolomites and surrounding areas located to the E of the Giudicarie lineament. Upper Cretaceous-early Eocene thick Flysch deposits of Lombardy and Giudicarie are well preserved along the Southern and Eastern border of the Pre-Adamello belt (S-verging Alpine orogen). Towards the E, in the Dolomites and in the Carnic Alps and external Dinarides, only incomplete remnants of Flysch deposits, Aptian-Albian and Turonian-Maastrichtian in age, are present. They can be considered as equivalent to those of Lombardy and Giudicarie formerly in connection along the N-Giudicarie corridor. All these deposits may correspond to the foredeep syntectonic sedimentary records of the S border of the new Cretaceous-Eocene orogenic belt of the Alps. Differences between the eastern and western blocks (the Dolomites versus the pre-Adamello belt) can be related to the Cretaceous-Eocene N Giudicarie transfer zone, which produced the basic structural setting discussed here. Due to these data and interpretations the Giudicarie bending of the Alps appears to be a late Mesozoic-early Tertiary tectonic inheritance rather than the result of the Neogene compressional evolution. During the late Eocene to early Oligocene the transfer zone was utilized for the ascent and emplacement of the Paleogene Adamello batholith. Oligocene to Neogene compressional evolution inverted the N-Giudicarie fault into a back-thrust of the Austroalpine units over the South-Alpine chain rearranging most of the former structural setting.

AbstractThe geological evolution of the Northern-Central Apennines has been strongly controlled by structural features inherited from pre-thrusting stages. The Apennines consist of a fold-and-thrust belt developed during Neogene time, involving sedimentary successions that were deposited within different paleogeographic domains. The paleogeographic evolution was controlled by the effects of syn-sedimentary tectonics that were active in the Triassic-Neogene time interval, and that are, from Trias to Neogene, related to different geodynamic settings. The Jurassic extensional phase favoured the dissecting of the Triassic carbonate platform and led to the development of different paleogeographic domains. Main oblique and trasversal faults, with transtensive kinematics, characterized the boundaries between different domains. After the Jurassic phase, from Cretaceous to Neogene, the Northern-Central Apennines were characterized by the development of ridges and depressions. These structures were affected by the development of normal fault systems, bending processes within the ridges, with uplift of the crestal sectors and tilting in the peripheripheral ones. The geometries and the structural setting of the foreland domains, of the foredeep and piggy back basins and of the Neogene Apenninic thrust belt are controlled by evolution of the former tectonic elements evolution. The development of extensional faults, the uplift and bending observed in the Apenninic sedimentary sequences during the convergence phase and during a part of the continental collision phase could represent distal effect of the dominant compressional regime. In this geodynamic domain the first tectonic inversion processes in a positive sense occurred along the pre-existing Jurassic listric faults systems.
The reactivation first affected the flat sectors of the fault planes and then progressively more superficial ones. In the upper sedimentary cover these processes favoured buckling, flexuring and faulting. Furthermore, during the subsequent involvement of the foreland domains in the foredeep and chain systems, the propagating thrust surface still reused former discontinuities both as a frontal and lateral ramp, completely inverting their movement.
During the compressional stage the west-dipping listric normal faults were reactivated in positive sense. The former east-dipping normal faults have been eastward rotated or offset by thrust faults.

AbstractThis study focuses on the Tertiary tectonic evolution at the boundary between Western Alps and northern Apennines in central Liguria (Italy). The architecture of the two belts derives from the oblique convergence between the Europe and Adria plates and hence this area represents an ideal case to study the crustal structures that develop during oblique lithospheric convergence. The analysis of the Oligocene-Miocene brittle structures reveals: the occurrence of principal displacement zones with related minor structures that fit a transpressional dextral regime and a NE-SW direction of maximum shortening; a regional strain partitioning between wrench-dominated and contraction-dominated domains; a structural control on the orientation and development of brittle structures by the pre-existing weaker pathways, provided by the alpine foliations and ductile shear zones.
The principal displacement zones can be easily framed in the Oligocene-Miocene geodynamics of the «Ligurian knot», where the right-hand strike-slip component of the system provided a release of the Ligurian Alps from their southeastern segment, thus allowing the tightening of the arc of the Western/Ligurian Alps.

AbstractIn the Northern Apennines, the Poggio Carnaio Sandstone Formation consists of sandy-clayey turbidites, cropping out in the northernmost corner of the Val Marecchia Nappe.
The formation has been considered Oligocene in age and is commonly interpreted as an Epiligurian unit, unconformably deposited above the Val Marecchia Nappe during its transport towards the Adriatic foreland.
The Poggio Carnaio Sandstone Fm rests on the Argille Varicolori Fm of the Val Marecchia Nappe, but field data do not allow it to be recognized wherever it abruptly replaces the pelagic sediments of the Argille Varicolori Fm, thus testifying to the foredeep evolution of the basin, or where it unconformably overlies this latter formation.
Nannofossil assemblages are characterized by abundant reworked Cretaceous and Paleogene taxa and by some taxa, whose first occurrence is reported in the upper part of the NN4 Zone = upper part of the CN3 Zone. Therefore the formation must be considered not older than Langhian.
Detrital modes of arenites revealed a quartz-feldspathic composition and the lithic component includes mainly metamorphic fragments and minor plutonic, sedimentary, ophiolithic and volcanic clasts. The presence of clasts of garnet, sillimanite, hornblende and glaucophane is significant. Biostratigraphic as well as petrographic data agree with the interpretation of the Poggio Carnaio Sandstone Fm as an Epiligurian succession.
Rock fragments indicate source areas characterized by Ligurian-, Pennidic- and Australpine-type units. Sedimentary facies and textural features of arenites, revealing a rapid erosion and deposition of clasts in a basin close to the source area of the clastic supply, indicate that the Alps cannot be considered as the source area of these arenites, as frequently argued for many North-Apennine clastic formations. Ligurian-, Pennidic- and Australpine-type units were located close to the Poggio Carnaio Sandstone basin, probably representing the geometrically highest units of the Palaeo-Apennine Chain.

AbstractRecent models propose that the exhumation of high-pressure rocks occurs by means of a return flow inside a subduction channel of low viscosity serpentinite between the confronting plates. Model predictions include different pressure-temperature paths and ages in the exhumed subduction complexes.
We studied a serpentinitic mélange in the Ligurian Alps to test this hypothesis. It contains exotic tectonic blocks with respect to the surrounding metaophiolites, which equilibrated at different peak metamorphic conditions and record different segments of a typical subduction P-T path. Both structural evidence and P-T paths of the different blocks suggest coupling between blocks and matrix in the blueschist facies.
We obtained 39Ar/40Ar ages for the eclogite facies peak (43.2±0.5 Ma) and for the blueschist facies peak (39.95±0.37 Ma and at 43.4±0.5 Ma) in different blocks; these data point to diachronous metamorphic trajectories and independent tectonic evolution of the different slices inside the channel. Inasmuch as the geochronological, petrographic and structural data fit the predictions of numerical models in terms of different pressure-temperature paths and variable metamorphic ages, we suggest that the studied mélange has been originated in the subduction channel. This mechanism can be extended to other serpentinitic mélanges in the Alps and other orogens, for which we expect further investigations will show a growing heterogeneity in the timing of metamorphic equilibration and of P-T paths.

AbstractIn the study area, located between Argentina Valley and Roya Valley, south of the village of Triora, the Meso-Cenozoic cover of the Argentera-Mercantour Crystalline Massif consists of marls and marly-clays, Campanian in age, that are overlain by the Paleogene unit named «Nummulitique».
This unit is composed of a transgressive upper Lutetian complex evolving into a Bartonian-Priabonian siliciclastic turbidite complex («Ventimiglia flysch»). The lower complex includes coarse grained siliciclastic, mixed and carbonate lithofacies of shallow marine environments (Capo Mortola calcarenite) grading upwards to deep marine marls (Olivetta San Michele silty marl). In the area, the nummulitic limestone is commonly made up of larger foraminifera-bearing calcarenite and calcirudite that, from South to North, laterally grade to oncolithic limestone (Loreto calcarenite member), mainly composed of rhodoliths and Acervulina macroids.
The Ventimiglia flysch can be regarded as a lateral equivalent of the «Grès d'Annot». The sedimentation of the lower and the upper complex is controlled by the tectonic events of the Ligurian Alps. The former deposits took place during the early evolution stage of the Ligurian Alps foredeep basin, whereas the turbidite deposits of Ventimiglia flysch record the basin filling phase. Evidences of this tectonic control are provided by the occurrence in the Ventimiglia flysch of olistoliths and olistostromes supplied by the chain front, and of slumping and synsedimentary folding.

AbstractPreservation of stratigraphic settings in continents is mostly confined to uppermost crustal levels, in which prevailing deformation is translational and internal strain of tectonic units is weak. This does not specially depend on association of metamorphism to tectonic processes, but rather on mechanical properties of deforming multilayers. Scattered findings of sedimentary features, not supported by structural investigation on the actual nature of lithologic layering, may lead to failure in determining size of preserved sedimentary sequences. In the intermediate and lower crust, interaction of metamorphism and deformation down to granular scale facilitates construction of new types of lithologic layers and segregation of thick differentiated mineral layerings that mimic stratigraphic sequences. Critical examples of difficulties encountered in different tectonic contexts when assessing the sedimentary origin and related stratigraphic meaning of variously deformed layered sequences are summarised. In deep subduction-collision zones similar or contrasted lithostratigraphies are of little help in definition of tectonic units; the structural and metamorphic reworking of rocks of contrasted origin constructs tectonic units that repeatedly couple and decouple from similar adjacent sequences and their actual relative mechanical paths may be disclosed by a combined structural and petrologic analytical tool delimiting volumes that experienced equivalent structural histories and metamorphic signatures (contouring of tectono-metamorphic units=TMUs); these units constitute valuable elements of correlation in metamorphic belts and for the investigation of mechanisms of lithosphere dynamics.

AbstractOphiolites crop out discontinuously in the Northern Calabrian Arc (Southern Italy). They consist of high pressure/low temperature metamorphic ophiolitic sequences of Late Jurassic-?Early Cretaceous age, in which a metabasic and metaultramafic association is the base of a complex metasedimentary cover ranging from pelagic to flyschoid type sediments. These ophiolitic sequences, interpreted as slices of oceanic lithosphere belonging to the Jurassic Tethys realm, occupy an intermediate position in the northern Calabrian Arc nappe pile, between the overlying Hercynian continental lithosphere (Calabride nappe) and the underlying Apenninic carbonate units.
In the literature, these ophiolitic sequences are subdivided into several tectonometamorphic units; some authors distinguished between an upper slightly metamorphic ophiolitic unit and a lower HP-metamorphic ophiolitic unit. This subdivision contrasts with new petrological data and geothermobarometric modelling. In fact, the overall P-T evolution for several ophiolitic sequences from the northern Calabrian arc describes comparable paths, characterized by a HP-LT metamorphism followed by retrogression under greenschist facies conditions. The metamorphic climax is calculated at pressures ranging between 0,9 and 1,1 GPa and a temperature around 380°C.
Moreover, structural analysis of rocks characterized by HP syn-metamorphic ductile deformation suggests that tectonic evolution is quite homogeneous and similar, although different degrees of deformation can be observed. The high-pressure mineral assemblage defines a pervasive foliation developed during a compressive tectonic event (D1) that transposed the earlier structures. A second tectonic event (D2) which occurred during decompression at 0,4 GPa, produced millimetre to decametre scale asymmetric folds. Later extensional brittle structures are responsible for final exhumation of the HP rocks.
The tectonometamorphic evolution of the ophiolitic sequences of Northern Calabrian Arc is well explained in a context in which the oceanic-derived rocks underwent subduction and exhumation as tectonic slices inside an accretionary wedge.

AbstractThe identification of a reliable geodynamic/tectonic model for the Italian region would be extremely useful for several practical purposes, in particular for quantifying the parameters to be used for seismic hazard assessment. In this work, we argue that the model presently adopted as a basis for elaborating the seismic classification of the Italian territory (MELETTI et alii, 2000) is not compatible with several major features of the observed deformation pattern and that, consequently, such choice should be reconsidered, taking into account an alternative geodynamic model that can much better explain the major tectonic events occurred in the central Mediterranean region since the late Miocene.

AbstractIn this paper we present the results of geological studies aimed at better constraining the recent tectonic activity in an area of the Sannio region, located along the axis of the Southern Apennines of Italy. The study area has repeatedly been affected by several historical destructive earthquakes whose genesis is still matter of debate. A multidisciplinary study was carried out in order to document evidence for recent surface activity of a NW-SE trending normal fault system, known in the literature as «Calore River Fault System». This fault system seems to have an essential role in the genesis of important historical earthquakes, such as the 1688 event. Structural analyses outline a stress field characterized by a mean NE-SW oriented extension, in accordance with breakout data and the recent seismicity, as well as published geological and geomorphological data. Geomorphological analyses, in particular the analysis of longitudinal profiles of fluvial terraces, reveal a clear tilting of the Calore River Valley terraces. Our results support the concept of the «Calore River Fault System» as an active normal fault system that plays a key-role in recent tectonic activity of the area.

AbstractGeological mapping, combined with macroscopic and microscopic structural analyses have been used to unravel the geometry and tectonic evolution of the Monti dell'Uccellina group (Southern Tuscany). A polyphase tectonic history has been recognized, characterized by three main tectonic events associated with the development of shear zones, folds and foliations. During the first tectonic phase, East verging F1 folds with axial plane foliation developed under very low-grade metamorphic conditions, as highlighted by illite crystallinity data and by the calcite-dolomite geothermometer.
Several piled tectonic units, belonging to the Tuscan and Subligurian domains, constitute the backbone of the Monti dell'Uccellina range.
These are, from bottom to top: 1) the Torre Cannelle Unit, made up by the Verrucano Group rocks; 2) the Talamone Unit, made up by the Calcare Cavernoso Formation; 3) the Monti dell'Uccellina Unit, represented by a passive margin sequence spanning from the Triassic Verrucano group at the base to the Tertiary Scaglia Fm. at the top; 4) the Vacchereccia Unit, represented only by Triassic Verrucano Group; 5) the Collelungo Unit, made up by the Calcare Nummulitico Fm. followed by the Macigno Fm; 6) the Canetolo Unit (Sub-Ligurian Unit Auctt.) represented by the «Argille & Calcari» Fm.
Stacking of the nappe pile occurred during the first tectonic phase (D1) in two stages: during the first stage the main tectonic units were emplaced. The second tectonic stage is characterized by later thrusts that cut through the older ones, all of them with a top-to-the- East sense of movement, that led to the emplacement of three tectonic complexes. Each complex comprises three superposed tectonic units that are from top to bottom the Collelungo Unit, the Vacchereccia Unit and the Monti dell'Uccellina Unit.
During the second tectonic phase (D2), the nappe pile was deformed by a kilometre-scale N-S trending upright antiform gently plunging towards the North.
The last tectonic phase is characterized by the development of sub-horizontal folds and of low-angle detachment faults that were produced during the post-collisional extensional events.
A detailed survey, that was achieved through compilation of a 1:10.000 scale map, has clarified the structural and stratigraphic position of the «Pseudoverrucano» Auctt. Formation, whose attribution has been debated for a long time. According to our data it can be referred to two different tectonic units: the Vacchereccia Unit, represented only by this formation, and the Monti dell'Uccellina Unit where it constitutes the bottom of a post-Triassic continental margin sequence.

AbstractThe behaviour of Sardinia and Corsica within the Alpine-Apennine orogenic events has not been considered in a univocal way; different hypotheses have been proposed, disregarding any eventual effect on the internal structuration of this piece of European crust.
Identifying the mechanism and age of the prominent strike-slip tectonics in Sardinia and Corsica allows us to bear new insights on the relationships between the south European crust and Adria plate. Syntectonic Oligocene-Aquitanian deposits fill some intracratonic basins in Sardinia. They developed in correspondence with releasing bends that affect the sinistral strike-slip faults, constraining the time span during which this tectonic regime was active.
Thrusts and folds involving the Mesozoic and Lower Cainozoic cover are not ubiquitous in Sardinia, they are mainly localised along deformed corridors in the NE part of the Island where deeply shortened Cainozoic conglomerates were involved in the wrench-thrust faults which, in some case, led the basement to override the Mesozoic cover. The association of these structures to restraining bends is documented, so that they are the coeval transpressive counterparts of the strike-slip basins.
Confining most of the Tertiary strike-slip tectonics of Sardinia and Southern Corsica within an Oligocene-Aquitanian time interval involves the following consequences:
i) no E-W extension, leading to a N-S trending rift (in present-day coordinates), was active in Sardinia and Corsica during Oligocene-Aquitanian times;
ii) the so-called Sardinia Rift is an assemblage of shallow asymmetric basins, trending N150, which developed during the late Burdigalian-Langhian, i.e. contemporary to the onset of the collapse of the North Apennine and Alpine Corsica orogenic wedge and to the opening of the North Tyrrhenian Sea;
iii) the Oligocene-Aquitanian strike-slip tectonics in Sardinia is consistent with the deformation of a hinterland involved in collision; this was the collision between Adria and Europe that led to the building of the North Apennines;
iv) the collisional event predates the drifting of the Sardinia-Corsica crust and the opening of the Liguro-Provencal basin.

AbstractThe architecture of the fault network and the late- to post-metamorphic structural evolution in the internal Cottian Alps have been studied by an integrated approach combining morphostructural analysis, field mapping and detailed mesostructural analysis between the Susa and Pellice Valleys. Available apatite fission track data indicate that this sector of the Western Alps reached shallow crustal levels, where brittle deformation mechanisms prevail, by Late Oligocene times. The analysed area comprises two main N-S striking regional, polyphasic semi-brittle to brittle deformation zones: the Colle delle Finestre Fault Zone (CFFZ) and the Col del Lis-Trana Deformation Zone (LTZ). The activity of those long-lived structures evolved, respectively, from dextral and dextral-reverse to extensional. In the block bounded by these two regional structures, the late- to post-metamorphic tectonic evolution is characterized by two faulting stages: (a) the development of an E-W left-lateral fault zone with a minor normal component of movement; at the regional scale, this fault zone may be considered as an antithetical shear of the major LTZ and the CFFZ; (b) the extensional reactivation and development of N-S normal faults, coeval with those recorded both by the LTZ and the CFFZ. The geometry of the fault and fracture systems has been compared with the remote sensed lineaments pattern, characterized by four main systems: Ln1 (N0°-30°E), Ln2 (N45°-70°E), Ln3 (N80°-100°E) and Ln4 (N100°-120°E). The lineament systems display similarities in terms of orientation, geometry and length with the fault systems observed at different scales. These similarities allowed us to extrapolate the structural model outlined in the mapped area to the adjoining sectors. Comparison between the different data suggests that the pattern of the lineaments detected between the LTZ and the CFFZ agrees with the architecture of a strike-slip fault network, which accommodated the internal deformation of the block bounded by these two major N-S transcurrent deformation zones. The transcurrent activity of these faults is here interpreted as coeval with the late dextral movements along the Canavese Line and with the propagation, in the Late Oligocene-Early Miocene, of the roughly E-vergent South-Alpine Thrusts beneath the Tertiary Piemonte Basin. The extensional event that followed may be related to the uplift with the subsequent isostatic readjustment of the chain which may have also induced the normal reactivation of the Penninic Frontal Thrust. This extensional regime is also in agreement with focal mechanisms of recent earthquakes.

AbstractGeological mapping and structural analysis carried out in the Sannio-Molise sector of the Southern Apennines provide a complete record of the polyphase deformation sequence affecting the succession of the Daunia Unit. These deposits represent an ancient foredeep turbiditic succession, deposited from Oligocene to upper Tortonian and involved in the Apennine tectonics since upper Tortonian times.
Two main contractional stages can be distinguished in the structural evolution of the Daunia Unit: the first deformation stage, which consists of initial layer-parallel-shortening and in the development of thrusts and metre- to decametre-scale wavelength folds (F1 and F2) developed in an extremely short time, between the upper Tortonian and pre-salinity crisis Messinian. The timing of this first deformation phase is well constrained by the presence of thrust-top Messinian-Pliocene deposits extensively outcropping in the studied area.
The second stage of the contractional deformation is characterized by gentle folds with sub-vertical axial surfaces (F3), metre- to hectometre-scale in wavelength, and breaching thrusts, active at least until the middle Pliocene.
Finally, the Daunia Unit has been affected by extensional tectonics characterized by the development of mainly NW-SE and NE-SW trending normal faults.

AbstractPresent knowledge on structure and petrology of the various masses of Alpine-Apennine ophiolitic peridotites provides evidence that Triassic-Jurassic rifting and spreading in the Ligurian-Piemontese domain was accomplished through successive stages of lithosphere evolution well recorded in the mantle peridotites.
The early stages of rifting, active during Triassic times, were dominated by overall extension and thinning of the continental lithosphere and exhumation of the sub-continental lithospheric mantle via km-scale extensional shear zones. This represents a tectonic-dominated stage.
Subsequent stages of rifting, starting from Early Jurassic times, were characterized by asthenosphere adiabatic upwelling and decompression melting triggered by lithosphere extension and thinning. These rifting stages were dominated by the interaction of tectonic and magmatic processes. MORB-type melts from the asthenosphere percolated through the overlying lithospheric mantle along the axial zone of the future oceanic basin and large volumes of the extending mantle lithosphere were modified by melt-rock interaction.
Melt percolation induced the thermo-mechanical erosion of the mantle lithosphere resulting in the weakening and softening of the lithosphere. It was a controlling factor in the transition from distributed continental deformation to localised oceanic spreading. MORB magmas intruded the sub-continental mantle along the axial zone of the future oceanic basin forming km-scale gabbroic bodies.
The oceanic stage (i.e. formation of the oceanic lithosphere) was characterized by complete failure of the continental crust during Late Jurassic times, and by the direct exposure of mantle peridotites on the sea-floor. Sub-continental peridotites were exposed at ocean-continent transition (OCT) zones and melt-modified sub-continental peridotites at more internal oceanic (MIO) settings.
MORB magmas reached the sea-floor, extruded above the mantle peridotites to form the oceanic lithosphere (i.e. the association of sub-continental peridotites and Jurassic MORB basalts) of the Ligurian Tethys basin.

AbstractThe aim of this investigation is to examine the relationship between springs and structural setting in the Mt. Cetona Ridge. This area represents an important regional morpho-tectonic feature oriented NNW-SSE, separated from the geothermal area of Monte Amiata to the West by the Radicofani Neogene Basin, and bounded to the East by the Valdichiana Neogene-Quaternary Basin. This Ridge is constituted by the Tuscan Nappe and the overthrusted S. Fiora Unit. New detailed field mapping and a structural study allowed recognition of a polyphase structural setting defined by four folding phases followed by three extensional and transtensional phases.
Coupled to the structural investigation, 13 spring water samples were collected in the area in May and in August 2005. Groundwater ranges from cold, low mineralized calcium-bicarbonate to warm, highly mineralised, calcium sulphate. Results are in general agreement with previous studies indicating the recharge area in the Cetona upland and a circulation in a highly fractured, quasi-continuous reservoir constituted by the Mesozoic limestone and the underlying Burano anhydrite formation. Geochemical modelling indicates that the high variability in the hydrochemical and isotopic composition cannot be explained by a simple binary mixing between two ground-water types, but rather reveals a geochemical evolution involving anhydrite and dolomite dissolution, and calcite precipitation. Outflows are closely related to the structural setting of the area and hydrochemistry allows discrimination of different fluids associated with specific hydrogeological circuits.
The interpretation of the structural setting for Mt. Cetona Ridge was obtained by fieldwork studies integrating geochemical data of both thermal and cold springs. Results of this investigation allow us to propose a new tectonic evolution and fluid circulation model for this area.

AbstractThe Tertiary Piedmont Basin (TPB) stretches along the Piedmont-Liguria border and is a late- to post-orogenic basin that evolved in a piggy-back position on the Monferrato thrust belt. Its depositional story is strongly controlled by tectonic and eustatic events. The basin was filled with mainly marine sediments (upper Eocene-upper Miocene), which unconformably overlie the Ligurian Alps and the Northern Apennines. The early stage of sedimentation of TPB records a transgressive phase (time-transgressive from the eastern to the western sectors, upper Eocene-upper Oligocene), characterized by the deposition of alluvial fan and fan delta siliciclastic conglomerates and sandstones, marine shallow-water coarse to fine grained siliciclastic sediments, and reef limestones.
The TPB reefal buildups, which developed close to the paleoshoreline, have a lower Rupelian-middle Chattian stratigraphic distribution and are restricted to the central part of the southern margin of the TPB. The Valzemola-San Bernardino reef is the younger and the westernmost settlement, while the Val Lemme reef represents the older and easternmost one.
The depicted stratigraphic and geographic distribution may be the result of a combined climatic and tectonic control. The lack of reef settlements west of Valzemola-Bric S. Bernardino may be due to climatic condition unfavourable for the reef development (temperature cooler than those of the early Rupelian-middle Chattian time interval). The absence of reefs in the area to the east of Val Lemme may be the consequence of bottom instability and high sedimentation rates (unfavourable conditions for the reef development) caused by the syn-sedimentary tectonic activity along the Scrivia fault, during the time interval spanning from the late Eocene to the early Oligocene (notwithstanding the favourable climatic conditions).
Finally, the age of the older reefal complex, i.e. early Rupelian (Val Lemme), gives an obvious constraint to the age of the end of the N-vergent thrusting phase of the Voltri Unit onto the flysch units and its sedimentary cover.

AbstractThis paper illustrates the results of structural studies carried out in the western margin of Tuscany along a major crustal structure. Surface deformation of sediments filling different basins aligned on top of this major structure (from north to south: the Fine Basin, the Sassa-Guardistallo basin, the Rio Guardigiano area in the Lustignano basin) allow us to date its tectonic activity to the Messinian-Early Pliocene. In these areas, structures such as reverse and strike-slip faults and mesoscopic folds are widely developed. Structural analysis determined a compressive stress field with the σ1 oriented from E-W to NE-SW active from Messinian to Early Pliocene. At the southern end of this crustal structure, the Gavorrano antiform and the granitic pluton (radiometric age of granite ∼4.4 Ma) coring this fold correlate with a thrust ramp anticline at depth, and thus constrain thrust activity to the Early Pliocene. These data document a Messinian-Early Pliocene compressive activity that contrasts with models invoking continuous extensional tectonics affecting the hinterland since the Late Oligocene-Middle Miocene in the frame of a back-arc-slab retreating process. The results presented therefore raise the question of which geodynamical model could account for such a complex structural evolution of Northern Apennines hinterland.

AbstractThe outermost, NE-verging fronts of the Northern Apennines (Italy) are overlain by a thick syntectonic sedimentary wedge filling up the basin beneath the Po Plain. Due to fast sedimentation rates and comparatively low tectonic rates, the fronts are generally buried. Evidence for their activity includes scattered historical and instrumental earthquakes and drainage anomalies controlled by growing buried anticlines. The largest earthquakes, up to Mw 5.8, are associated with active compression, with a GPS-documented shortening rate <1 mm/a.
We used geological, structural and morphotectonic data to draw a N-S-striking section between Bologna and Ferrara, aimed at analyzing whether and how the deformation is partitioned among the frontal thrusts of the Northern Apennines and identifying the potential sources of damaging earthquakes. We pointed out active anticlines based on the correspondence among drainage anomalies, historical seismicity and buried ramps. We also analyzed the evolution of the Plio-Quaternary deformation by modeling in a sandbox the geometry, kinematics and growth patterns of the thrust fronts.
Our results (i) confirm that some of the main Quaternary thrusts are still active and (ii) highlight the partitioning of deformation in the overlap zones. We note that the extent and location of some of the active thrusts are compatible with the location and size of the main historical earthquakes and discuss the hypothesis that they may correspond to their causative seismogenic faults.